\documentclass[]{article}
\setlength{\pdfpagewidth}{8.5in} \setlength{\pdfpageheight}{11in}
\begin{document}
\begin{tabular}{lcccccc}
\multicolumn{7}{c}{Impact of treatment assignment on standardized test scores} \\ \hline
 & (1) & (2) & (3) & (4) & (5) & (6) \\
VARIABLES & Overall score & Overall score & Principal score & Principal score & Subsidiary score & Subsidiary score \\ \hline
 &  &  &  &  &  &  \\
Treatment & 0.16** & 0.13*** & 0.16** & 0.13** & 0.10 & 0.13** \\
 & (0.07) & (0.05) & (0.08) & (0.05) & (0.06) & (0.05) \\
Age &  & -0.03 &  & -0.02 &  & -0.04 \\
 &  & (0.02) &  & (0.02) &  & (0.02) \\
Female &  & 0.06 &  & 0.13** &  & 0.03 \\
 &  & (0.05) &  & (0.05) &  & (0.06) \\
STEM &  & 0.56*** &  & 0.22*** &  & 0.46*** \\
 &  & (0.06) &  & (0.06) &  & (0.07) \\
Mock overall score &  & 0.76*** &  &  &  &  \\
 &  & (0.03) &  &  &  &  \\
Mock principal score &  &  &  & 0.70*** &  &  \\
 &  &  &  & (0.03) &  &  \\
Mock subsidiary score &  &  &  &  &  & 0.39*** \\
 &  &  &  &  &  & (0.03) \\
Constant & 1.26*** & 0.73* & 1.15*** & 0.73* & 1.43*** & 1.53*** \\
 & (0.09) & (0.41) & (0.10) & (0.42) & (0.09) & (0.47) \\
 &  &  &  &  &  &  \\
Observations & 708 & 708 & 708 & 708 & 708 & 708 \\
 R-squared & 0.19 & 0.62 & 0.16 & 0.59 & 0.28 & 0.49 \\ \hline
\multicolumn{7}{c}{ Robust standard errors in parentheses} \\
\multicolumn{7}{c}{ *** p$<$0.01, ** p$<$0.05, * p$<$0.1} \\
\end{tabular}
\end{document}
